JP2010245465A - Nitride-based semiconductor laser and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride-based semiconductor laser of high reliability and high output by forming a window region without deteriorating contact resistance, in a laser process where a nitrogen material gas containing a hydrazine derivative is used for crystal growth of p-type layer of a nitride semiconductor. <P>SOLUTION: In this method of manufacturing the nitride semiconductor laser, an n-type cladding layer 2, an n-type guide layer 3, an active layer 4 and an undoped guide layer 5 are formed on an n-type GaN substrate in an MOCVD method. An SiO<SB>2</SB>film 15 is formed as an impurity-supplying source on the same layer 5, and the entire surface is covered with a protective film 16. By performing high-temperature heat treatment of about 1,100°C or above, an n-type impurity solid phase diffusion region 11 is formed by diffusing Si, and the window region 12 is selectively formed in the active layer 4 of the vicinity region of a planned part 14 for forming a laser end surface. After removing both the films 15 and 16, a p-type layer is grown on the laminated guide layer 5 with an Mg as a dopant and an ammonia and an hydrazine dielectric as a nitrogen-supplying source by the MOCVD method. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor laser manufacturing technique and a nitride semiconductor laser manufactured by the manufacturing technique.

  A nitride-based semiconductor laser diode (hereinafter, the laser diode is referred to as “LD”) is used as a semiconductor laser for recording / reading a Blu-ray disc. In order to improve the recording speed and to promote the multi-layer recording for increasing the recording density, it is necessary to further increase the output of the nitride semiconductor LD.

In such a nitride-based semiconductor LD, as a technology important for realizing a high-power operation in which the output of the laser light exceeds 400 mW,
1) Suppressing the operating voltage by reducing the resistance of the electrode part, and
2) The suppression of end face destruction by reducing light absorption at the end face of the laser resonator can be mentioned.

  In order to suppress deterioration over time during a high output operation, it is necessary to reduce the operating voltage by suppressing a voltage drop generated at the contact portion of the electrode.

  The contact resistance of the p-side electrode greatly depends on the carrier concentration of the contact layer corresponding to the p-type uppermost layer, the trap concentration at the interface, and the work function of the electrode material.

  When a nitride-based semiconductor layer is grown by metal organic chemical vapor deposition (hereinafter referred to as “MOCVD”), when Mg is doped as a dopant for the growth of a p-type layer, the nitrogen source ammonia is Hydrogen generated by decomposition is taken into the crystal and enters the site next to Mg, thereby preventing activation. Therefore, in order to obtain a p-type crystal, an annealing process at 600 ° C. or higher is required after the growth of the p-type doped layer in an atmosphere without hydrogen. In this p-type annealing treatment, nitrogen escape from the surface and surface oxidation are accompanied, so that n-type carriers due to nitrogen defects are generated on the crystal surface, or the trap concentration increases, so that the p-side electrode There is a problem that the contact resistance of the device deteriorates.

  As a method for solving this problem, a method of performing crystal growth using a hydrazine derivative during the growth of a p-type layer has been proposed (see Patent Document 1). According to this method, since incorporation of hydrogen into the crystal is suppressed, sufficient p-type conduction characteristics can be obtained without performing the p-type annealing treatment after the growth of the p-type doped layer. Further, in such a crystal, since there is no surface degradation that occurs during the above-described p-type annealing treatment, the contact resistance can be reduced compared to a normal crystal subjected to the p-type annealing treatment. Is possible.

  On the other hand, as a factor governing the maximum output of the laser, there is a problem of end face destruction due to light absorption at the end face of the laser resonator. In order to prevent this point, the structure of a red LD having a window region (optical non-absorption window region) that reduces the absorption of laser light at the end surface by widening the band gap of the end surface has been developed so far. Has been adopted. Therefore, it is expected that the use of a structure having the same optical non-absorption window region is effective in the nitride semiconductor LD in order to suppress the end face breakdown and increase the maximum output. The

  As a method for widening the band gap, it is common to disorder the multi-quantum well (hereinafter referred to as “MQW”) in the active layer to form a mixed crystal and obtain a band gap higher than the quantum well level. Therefore, a similar method has been proposed for the nitride semiconductor LD.

  For example, in order to selectively disorder the windows, a method of disordering by solid phase diffusion (see Patent Document 2), a method of disordering by ion implantation + annealing (see Patent Document 3). Etc. are mentioned as a preceding example.

  Alternatively, there is a prior example (see Patent Document 4) that defines the distribution of impurities regardless of the method.

  In any of these preceding examples, the interdiffusion temperature of the constituent elements is reduced by locally diffusing impurities in a range including the MQW active layer in the window forming region, thereby achieving selective disordering.

Japanese Unexamined Patent Application Publication No. 2009-16452 JP 2006-140387 A JP 2006-229210 A JP 2007-214361 A

  In the case of forming a window region structure as described above in a crystal such as a nitride-based semiconductor in which diffusion of impurities is not easy, a high-temperature heat treatment exceeding the crystal growth temperature is required. However, such high-temperature heat treatment causes unnecessary diffusion of dopant impurities and degrades the laser oscillation characteristics or the crystal surface, which adversely affects the subsequent processes.

  In particular, when a p-type layer is grown using the hydrazine derivative proposed in Patent Document 1, the high-temperature heat treatment for forming the structure of the window region is performed after the growth of the p-type layer. By doing so, the merit of the low contact resistance peculiar to the growth film using hydrazine described above is lost, and the operating voltage may increase.

  The present invention has been made in recognition of such a technical situation, and its main object is a process using a nitrogen source gas containing a hydrazine derivative for crystal growth of a p-type uppermost layer of a nitride semiconductor laser. In order to realize an increase in the maximum output of the laser by making it possible to form the structure of the window region while realizing a reduction in the operating voltage (energy saving) without deteriorating the contact resistance of the p-side electrode. It is in providing the manufacturing method of. In addition, the present invention provides a method for forming the structure of the window region while suppressing the deterioration of the epitaxially grown film by high-temperature heat treatment exceeding the epitaxial growth temperature at the time of forming the window region, and maintaining the basic characteristics of the laser. The main purpose is to provide

  The method for manufacturing a nitride-based semiconductor laser according to the present invention includes an n-type doped layer process for forming an n-type doped layer on a substrate, and an undoped layer for forming an undoped layer including an active layer on the n-type doped layer. A hydrazine derivative after the forming step, a window region forming step with a heat treatment for changing optical characteristics at a predetermined position of the active layer to be a window region of the nitride semiconductor laser later, and the window region forming step A p-type uppermost layer forming step of forming a p-type uppermost layer on the undoped layer at a temperature equal to or lower than the maximum heat treatment temperature of the window region forming step using a gas containing the p-type uppermost layer; And a step of forming a side electrode.

The nitride semiconductor laser according to the present invention includes a substrate, an n-type doped layer provided on the substrate, an undoped layer including an active layer provided on the n-type doped layer, and the active layer. A p-type top layer provided on the undoped layer, and a p-side electrode in contact with the p-type top layer, the p-type top layer The carbon concentration of the p-type is 5 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ¹⁸ cm ⁻³ or less, and the concentration of the p-type impurity in the p-type uppermost layer is twice that of the p-type impurity near the center of the nitride semiconductor laser. It is characterized by being less than.

  According to the subject of the present invention, the p-type uppermost layer grown by using hydrazine can be free from thermal damage due to the formation of the window region, so that the contact characteristics of the p-side electrode in contact with the p-type uppermost layer are deteriorated. It is possible to increase the maximum output of the laser by forming a window region on the laser end face while reducing the operating voltage of the laser.

  Therefore, according to the subject of the present invention, it is possible to obtain a long-lived high-power laser without degrading the basic laser characteristics.

  Hereinafter, various embodiments of the present invention will be described in detail along with the effects and advantages thereof with reference to the accompanying drawings.

FIG. 3 is a front view schematically showing the structure of the nitride-based semiconductor laser device according to each of the first, second, and fifth embodiments when viewed from the emission end face side. FIG. 2 is a longitudinal sectional view schematically showing an element structure (stripe structure) when the element of FIG. 1 is cut along a plane perpendicular to the paper surface of FIG. 1 along the disconnection shown in FIG. 1. FIG. 3 is a longitudinal sectional view showing a manufacturing process of the nitride semiconductor laser according to the first embodiment (after the epitaxial growth). FIG. 3 is a longitudinal sectional view showing a manufacturing process of the nitride semiconductor laser according to the first embodiment (enlarged view after epitaxial growth). FIG. 6 is a longitudinal sectional view showing a manufacturing process of the nitride semiconductor laser according to the first embodiment (impurity diffusion process diagram for forming a window region). It is a longitudinal cross-sectional view which shows typically the structure of the stripe part provided with the undoped AlGaN guide layer which is laminated | stacked on the film | membrane of the original undoped AlGaN, and has a comparatively thick film thickness. FIG. 5 is a longitudinal sectional view showing a manufacturing process of the nitride semiconductor laser according to the first embodiment (a view after p-type layer growth by MOCVD again). FIG. 3 is a longitudinal sectional view showing a manufacturing process of the nitride semiconductor laser according to the first embodiment (a view after forming a p-side electrode and an n-side electrode). FIG. 3 is a longitudinal sectional view showing a manufacturing process of the nitride semiconductor laser according to the first embodiment (after completion of the wafer process). It is a top view which shows the laser structure manufactured using the manufacturing method which concerns on Embodiment 1 of this invention. It is a perspective view which shows the laser structure manufactured using the manufacturing method which concerns on Embodiment 1 of this invention. It is a figure which shows the electric current-output characteristic of LD which formed the window area | region, and LD which does not form a window area | region. It is a longitudinal cross-sectional view which shows the manufacturing process of the nitride-type semiconductor laser which concerns on Embodiment 2 (impurity diffusion process figure for window region formation).

(Embodiment 1)
FIG. 1 is a front view schematically showing the structure of the nitride-based semiconductor laser device according to the present embodiment as viewed from the emission end face side. 2 is a longitudinal section schematically showing a structure (stripe structure) when the element is cut along a plane perpendicular to the paper surface of FIG. 1 along the broken line A1-A2 in FIG. It is. 1 and 2 are also used in the second and fifth embodiments in which the window region is formed by solid phase diffusion of impurities described later.

  The nitride semiconductor laser element illustrated in FIGS. 1 and 2 is, for example, a gallium nitride semiconductor laser element that generates blue-violet laser light.

As shown in FIGS. 1 and 2, an n-type AlGaN cladding layer 2, an n-type GaN guide layer 3, and In _x are formed on the surface (first main surface) of an n-type GaN substrate 1 that is an n-type nitride semiconductor substrate. Ga _(1-x) N / In _y Ga _(1-y) N (x> y, x> 0, y ≧ 0) Multiple quantum well (MQW) active layer 4, undoped AlGaN guide layer 5, p-type AlGaN cladding The layer 6, the p-type GaN contact layer 7, the insulating film 8, and the p-side electrode 9 are disposed by sequentially laminating a part of the film. An n-side electrode 10 is disposed on the back surface (second main surface) of the n-type GaN substrate 1. Then, the MQW active layer 4 in each laser end face portion is selectively mixed with the n-type impurity solid phase diffusion region 11 to form a disordered region. A window region 12 having a wide band gap is selectively provided so as to function as an optical non-absorption region that does not absorb the generated laser light generated by the laser element. A portion composed of the n-type AlGaN cladding layer 2 and the n-type GaN guide layer 3 is referred to as an “n-type doped layer”, and an MQW active layer (first undoped layer) 4 and an undoped AlGaN guide layer (second undoped layer) 5. The portion consisting of is referred to as an “undoped layer”. Further, a portion composed of the p-type AlGaN cladding layer 6 and the p-type GaN contact layer 7 is referred to as a “p-type doped layer”. Therefore, the p-type GaN contact layer 7 corresponds to the “p-type top layer”. It is also possible to use sapphire as an insulator instead of the n-type GaN substrate 1 by a method such as connecting the n-side electrode 10 to the n-type doped layer. The undoped AlGaN guide layer 5 may be an n-type with a low impurity concentration. Here, undoped (undoped type) refers to a material to which no impurity is intentionally added.

Here, the point described as “AlGaN” means a mixed crystal of the form Al _x Ga _(1-x) N (0 ≦ x <1), and x takes a certain value. . Unless x is specified, each AlGaN has a different value of x.

  A method for manufacturing the nitride semiconductor laser shown in FIGS. 1 and 2 will be described below with reference to FIGS. 3 to 8 which are longitudinal sectional views of the stripe portion similar to FIG.

(1) MOCVD growth On the Ga surface of the n-type GaN substrate 1 obtained by previously cleaning the surface of the GaN substrate by thermal cleaning or the like, an n-type AlGaN cladding layer 2, n is formed by a normal source gas by MOCVD. -type GaN guide layer _{3, In x Ga (1-} x) N / In y Ga (1-y) N (x> y, x> 0, y ≧ 0) MQW active layer 4, and a thin undoped AlGaN guide layer Each layer of 5 is grown sequentially.

  In this example, the layer 5 is grown so that the film thickness of the undoped AlGaN guide layer 5 at this stage is 20 nm.

The undoped layer (second undoped layer) on the MQW active layer 4 is In _x Ga _(1-x) N / In _y Ga _(1-y) N (x> y, x> 0, y ≧ 0) The guide layer is not limited to the undoped AlGaN guide layer 5 and may be a guide layer having an undoped GaN guide layer or a laminated structure of undoped GaN and undoped AlGaN.

The film thickness of the undoped AlGaN guide layer 5 on such an In _x Ga _(1-x) N / In _y Ga _(1-y) N (x> y, x> 0, y ≧ 0) MQW active layer 4 is From the viewpoint that if the thickness of this layer is too thin, the function as a protective film on the surface of the MQW active layer 4 will not be exhibited. Conversely, if the thickness of this layer becomes too thick, the laser light is emitted into the MQW active layer 4. From the viewpoint of the optical properties of the laser that it is impossible to confine, it is desirable that the value be in the range of 10 nm or more and less than 100 nm.

  The growth of the undoped layer composed of the guide layer 5 having such a structure and film thickness value suppresses the deterioration of the MQW active layer 4 during the high-temperature heat treatment for impurity diffusion described above, and causes an increase in operating voltage. It is possible to realize a window region with no optical loss and to prevent the fundamental oscillation characteristics of the laser from being impaired.

  Here, FIG. 3 is a longitudinal sectional view schematically showing the structure of each of the layers 2 to 5 after the epitaxial growth, and FIG. 4 is an enlarged view of a region near the MQW active layer 4 surrounded by a broken line BL. It is a longitudinal cross-sectional view. Reference numeral 14 in FIG. 4 indicates a laser end face formation scheduled portion.

  The growth temperature at the time of crystal growth by MOCVD so far is, for example, 750 ° C. when the MQW active layer 4 is grown, and 1000 ° C. when the other layers are grown.

(2) Formation of Window Region Next, a process of selectively generating defects in the laser end face formation scheduled portion 14 and its surrounding portion in the MQW active layer 4 (this process is a “selective disordering attraction method”). Say).

In an example of the present embodiment, a SiO ₂ film having Si as a constituent element as one of n-type impurities is used as a diffusion source. For this reason, the SiO ₂ film 15 is left only on the portion 14 to be the end face and its peripheral region in the upper surface of the thin undoped AlGaN guide layer 5. Then, a protective film 16 made of AlN or the like not containing Si is formed on the entire exposed surface from above the SiO ₂ film 15.

After that, high-temperature heat treatment for selectively diffusing Si as an n-type impurity in the vicinity of the laser facet formation scheduled portion 14 in the MQW active layer 4 is performed in an N ₂ gas atmosphere. Here, the heat treatment temperature for this purpose is a temperature in the range of 1100 ° C. or more and 1400 ° C. or less (if the heat treatment temperature exceeds 1400 ° C., the disordered region cannot be selectively formed in the MQW active layer 4). ), The heat treatment time is 30 minutes. Note that the diffusion of impurities can be promoted by adding a gas containing hydrogen to the N ₂ gas atmosphere.

  The enlarged structure after the Si diffusion treatment is schematically shown in FIG. In FIG. 5, reference numeral 11 is an n-type impurity solid phase diffusion region generated by diffusion of Si in each of the layers 5, 4, and 3. When Si diffuses in the MQW active layer 4, the MQW active layer 4 is selectively mixed, so that the window region 12, which is a disordered region having a band gap that does not absorb laser oscillation light, is converted into a laser. It is selectively formed in the MQW active layer 4 in the vicinity of the end face formation scheduled portion 14.

  Instead of diffusing Si as an n-type impurity, as the selective disordering induction method, at least one impurity of a group of n-type impurities composed of B, C, O, P, S, and Si is used. It may be selectively diffused (in this case, a film containing the element as a constituent element is formed) or ion implantation described later may be selectively performed.

(3) Re-growth pretreatment Thereafter, both the SiO ₂ film 15 and the protective film 16 which are diffusion sources are removed using a hydrofluoric acid-based etching solution.

  Next, in order to clean the surface of the undoped AlGaN guide layer 5 after removing both the films 15 and 16, a heat treatment before the growth of the p-type layer is performed. The heat treatment temperature at this time is the same as or slightly higher than the p-type layer growth temperature (for example, 1050 ° C.) described later.

(4) Growth of p-type layer First, an undoped AlGaN film 55 is further laminated on the exposed upper surface of the thin undoped AlGaN guide layer 5 after cleaning by the MOCVD method to match the original undoped AlGaN film 5. An undoped AlGaN guide layer 5 having a relatively thick film thickness is grown (see FIG. 6). Note that the execution of the growth process to compensate for the shortage of the undoped AlGaN guide layer 5 is arbitrary and may be unnecessary.

  Thereafter, Mg is doped and the MOCVD method is performed again to grow a p-type layer composed of the p-type AlGaN cladding layer 6 and the p-type GaN contact layer 7 on the upper surface of the undoped AlGaN guide layer 5. At this time, in addition to ammonia, a hydrazine derivative is simultaneously supplied as a nitrogen supply source (a group V gas containing ammonia and a hydrazine derivative is used). At this time, for example, the supply molar ratio of the hydrazine derivative to the Group III raw material is 10 and the supply molar ratio of ammonia to the hydrazine derivative is 100. The region for supplying the hydrazine derivative and ammonia at the same time may be the entire p-type layer region (6 + 7) or only the p-type GaN contact layer 7 which is the p-type uppermost layer.

  In addition, the processing temperature in the MOCVD method for p-type layer growth is, for example, about 1050 ° C., and is relatively lower than the temperature of the high-temperature heat treatment at the time of forming the window region described above by at least 100 ° C. Crystal regrowth after the window region forming step is performed. This also applies to Embodiments 2 and 5 described later.

  Here, FIG. 7 is an enlarged view of the structure when a p-type layer composed of a p-type AlGaN cladding layer 6 and a p-type GaN contact layer 7 is grown on the upper surface of the undoped AlGaN guide layer 5 as in FIG. FIG.

(5) Wafer process After the growth of the p-type layer, a wafer process is performed by an ordinary method. However, the annealing process for p-type is not performed here. For the formation of the p-side electrode 9, Pd is used for the first layer, and the sintering process after the formation is not performed or the sintering process temperature is set to 450 ° C. or lower. When the front side process is completed, the back side process is performed.

  Regarding the formation of the back-side electrode, for example, Ti / Pt / Au is formed in this order, and the Si-containing plasma treatment is performed before forming the electrode, whereby the low-resistance n-side electrode 10 can be formed.

  Here, FIG. 8 shows a longitudinal sectional structure of the stripe portion after the wafer process is completed.

  When the wafer process is completed, a laser end face is formed by cleaving. At that time, cleaving is performed at a position where the structure of the window region 12 is divided into two equal parts as in the cross-sectional structure of the stripe portion shown in FIG. Thereby, the mirror end surface shown in the top view of FIG. 10 and the perspective view of FIG. 11 is obtained. As shown in FIGS. 10 and 11, the portion of the MQW active layer 4 in the mirror end surface and the vicinity thereof is the window region 12 described above. In FIG. 10 and FIG. 11, reference numeral 13 indicates a ridge waveguide.

  Thereafter, each nitride semiconductor laser element formed on the wafer of the n-type GaN substrate 1 is separated into chips and assembled in a predetermined process, thereby completing a laser diode.

The nitride-based semiconductor laser device having the window region 12 structure on the mirror end face produced by the manufacturing method as described above similarly has the window region structure on the mirror end face produced by the normal manufacturing method. It differs from the nitride semiconductor laser device in the following points. In other words, this element has 1) a carbon concentration in the p-type GaN contact layer 7 in the range of 5 × 10 ¹⁶ cm ^{−3 to} 1 × 10 ¹⁸ cm ⁻³ , and 2) laser light emission. The p-type impurity concentration of the p-type GaN contact layer 7 in the vicinity of the end face is within the range of in-plane variation in the stripe portion of the p-type impurity concentration when the contact layer is grown by the epitaxial layer alone. Have. For example, regarding the latter feature 2), the p-type impurity concentration of the p-type GaN contact layer 7 near the laser light emission end face is the p-type impurity concentration value of the contact layer 7 near the laser center. No more than 2 times (less than 2 times).

  Thus, since the window region 12 is formed prior to the growth of the p-type layer (6 + 7) using the hydrazine derivative together with ammonia as a nitrogen supply source, the p-side electrode is formed on the surface of the p-type layer without deterioration. 9 can be formed, and the contact resistance of the p-side electrode 9 can be kept low. As a result, the structure of the window region 12 without light loss can be realized without increasing the operating voltage (energy saving). . In addition, since the diffusion of the p-type dopant into the active layer 4 due to the high-temperature heat treatment in the process of forming the window region 12 can be avoided, a situation in which the laser characteristics are deteriorated can be avoided.

  As a result, it is possible to achieve high output and high reliability of the nitride-based semiconductor laser device. Here, FIG. 12 shows current-light output characteristics when the window region structure is provided and when the window region structure is not provided.

  Although the case where the active layer is the MQW active layer 4 is shown in the present embodiment, the active layer is not necessarily required to be MQW, and may have a single quantum well structure.

(Embodiment 2)
The feature of the present embodiment is that an AlN protective layer 17 is further formed on the undoped AlGaN guide layer 5 in the (2) window region forming step in the first embodiment. Other steps are the same as those in the first embodiment.

  FIG. 13 is a diagram schematically showing an enlarged vertical cross-sectional structure after the diffusion process for forming the window region 12 in this case. In this example, the AlN protective layer 17 is formed using a crystal growth apparatus. In the growth process of the AlN protective layer 17, ammonia and a hydrazine derivative are simultaneously supplied as nitrogen supply sources, and the growth temperature at that time Is set to 600 ° C. or lower. By forming the AlN protective layer 17 under such conditions, the AlN protective layer 17 after film formation has a polycrystalline or amorphous structure. Alternatively, the AlN protective layer 17 may be formed by another method such as sputter film formation by taking out the wafer separately from the crystal growth apparatus. The film thickness of the AlN protective layer 17 is set to a value within the range of 20 nm to 100 nm.

Then, after the high-temperature heat treatment for selectively forming the window region 12 in the MQW active layer 4, the AlN protective layer 17 is removed together with the SiO ₂ film 15 and the SiN protective film 16.

  According to the present embodiment, since the window region forming step is performed prior to the p-type layer growth step using the hydrazine derivative, the p-side electrode 9 having no deterioration can be formed on the p-type layer surface. As a result of the contact resistance of the side electrode 9 being kept low, a window region free from light loss can be realized on the laser end face without increasing the operating voltage. Moreover, the diffusion of the p-type dopant into the MQW active layer 4 due to the high-temperature heat treatment in the step of forming the window region 12 can be avoided, but the AlN protective layer 17 further deteriorates the surface of the MQW active layer 4. Therefore, the quality of the MQW active layer 4 can be maintained at a higher level, and the high output and high reliability of the nitride semiconductor laser can be realized without deteriorating the laser characteristics. It becomes possible.

(Embodiment 3)
The feature of the present embodiment is that, in the step of forming the window region of the first or second embodiment (2), for example, by selectively performing ion implantation of Si instead of solid phase diffusion of impurities, This is in that a region to be formed with the window region 12 is formed. Other steps are the same as the corresponding steps already described in the first embodiment. To that extent, the reference numerals used in Embodiment 1 are used.

That is, after epitaxial growth of each layer 2 to 5, a SiN film (not shown) is formed on the entire upper surface of the undoped AlGaN guide layer 5 to protect the surface of the MQW active layer 4. On top of this, a resist (not shown) having an opening only in a portion corresponding to the laser end face formation planned portion 14 and its peripheral region is formed as an implantation mask, and Si ions are implanted on the entire surface thereof. . Regarding ion implantation conditions at that time, for example, the energy of Si ions is 50 keV, and the dose of Si ions is 1E16 cm ⁻² . By this Si ion implantation, Si ions are introduced into the MQW active layer 4 in the portion corresponding to the laser end face formation scheduled portion 14 and its surrounding region.

  Thereafter, high-temperature heat treatment at a temperature in the range of 1100 ° C. or higher and 1400 ° C. or lower is performed in an atmosphere of hydrogen gas and nitrogen gas, and the portion of the MQW active layer 4 corresponding to the laser end face formation scheduled portion 14 and its surrounding region By causing interdiffusion between Si ions localized in each other, a window region 12 as a disordered region is selectively formed in the same portion of the MQW active layer 4. Therefore, the high-temperature heat treatment step performed after the Si ion implantation step is “a window region that does not absorb laser oscillation light with a high-temperature heat treatment at a temperature exceeding the crystal growth temperature of the p-type uppermost layer. This corresponds to the “high temperature heat treatment” in the “step of selectively forming in the MQW active layer 4 located in the lower layer”. Note that the high-temperature heat treatment time at this time is shorter than the high-temperature heat treatment time in the window region forming step in the first or second embodiment.

  As the implanted ions, in addition to one kind of Si, it is possible to use an element of at least one kind of impurity among a group of n-type impurities made of B, C, O, P, S, Si or the like. is there.

  According to the manufacturing method of the present embodiment, the window region 12 having no optical loss can be realized without causing an increase in operating voltage, and the window region 12 can be obtained by the diffusion of impurities in the first or second embodiment. Compared with the case of forming the window region 12, the time of the high-temperature heat treatment process for forming the window region 12 can be shortened, so that the deterioration of the crystal can be further suppressed and the laser oscillation can be performed without impairing the efficiency. In addition, it is easier to realize high output and high reliability of the nitride semiconductor laser.

(Embodiment 4)
The feature of the present embodiment is that, instead of solid phase diffusion of impurities in the step (2) window region forming step of the first embodiment, a pulse laser beam or a high energy electron beam is used after the growth of each layer 2 to 5. The window region 12 is selectively formed in the MQW active layer 4 by performing high-temperature heat treatment after selective irradiation. Other steps are the same as the corresponding steps already described in the first embodiment. Therefore, in each case, the reference numerals used in the first embodiment are used.

  (2) In the window region forming step, first, a pulse laser beam or a high-energy electron beam is selectively irradiated to the portion corresponding to the laser end face formation scheduled portion 14 and its surrounding region in the MQW active layer 4. Thus, lattice defects are locally formed in the same part.

  After the selective irradiation with the pulse laser beam or the electron beam, high-temperature heat treatment is performed in a temperature range of 1100 ° C. or higher and 1400 ° C. or lower in an atmosphere of hydrogen gas and nitrogen gas, so that the laser facet formation planned portion 14 and its surroundings Lattice defects existing locally in the portion of the MQW active layer 4 corresponding to the region are interdiffused to change the same portion of the MQW active layer 4 into a disordered region that functions as the window region 12. Therefore, the high-temperature heat treatment step after selective irradiation with pulsed laser light or high-energy electron beam is “a window that does not absorb laser oscillation light accompanied by high-temperature heat treatment at a temperature exceeding the crystal growth temperature of the p-type uppermost layer. This corresponds to the “high temperature heat treatment” in the “step of selectively forming a region in the MQW active layer 4 located under the p-type uppermost layer”.

  According to the manufacturing method of the present embodiment, the window region 12 without light loss can be realized without causing an increase in operating voltage, and the window region 12 can be formed by impurity diffusion as in the first or second embodiment. Since there is no light absorption by impurities compared to the case of forming, laser oscillation can be performed without impairing efficiency, and higher output and higher reliability of the nitride semiconductor laser can be realized more easily.

(Embodiment 5)
In the first embodiment, the formation process of the window region 12 is performed before the growth of all the p-type layers, but in this embodiment, a part of the p-type layers is grown. A process for forming the window region 12 is performed later. Impurities used for selective diffusion are p-type impurities.

(1) MOCVD growth First, an MOCVD method is used to form an n-type AlGaN cladding layer 2, an n-type GaN guide layer 3, In _x Ga _(1-x) N / In _y on the Ga surface of the n-type GaN substrate 1. The Ga _(1-y) N (x> 0, y ≧ 0) -MQW active layer 4, the undoped AlGaN guide layer 5, and the p-type AlGaN cladding layer 6 are sequentially formed. Incidentally, as already described in the second embodiment, an AlN protective layer 17 may be further added.

(2) Formation of Window Region Next, selective p-type impurity diffusion processing is performed.

  In the present embodiment, MgO is used as a diffusion source. Therefore, the MgO film is formed entirely on the upper surface of the p-type AlGaN cladding layer 6 which is the uppermost layer at this stage, and then a laser end face formation scheduled portion in the upper surface of the same layer 6 by etching treatment. The MgO film is left only on the portion corresponding to 14 and its neighboring region. Thereafter, the SiN protective film 16 is formed over the entire surface so as to cover the entire exposed surface of the remaining MgO film.

  Instead of selectively forming the window region 12 by diffusion of Mg, which is a p-type impurity from the MgO film, as described in the third embodiment, Mg ion implantation of the p-type impurity and the subsequent steps are performed. Similarly, it is possible to selectively form the window region 12 in the MQW active layer 4 without deteriorating the surface of the MQW active layer 4 by performing the high temperature heat treatment.

As the high-temperature heat treatment for impurity diffusion, the high-temperature heat treatment is performed in an atmosphere of N ₂ gas and at a temperature higher than the growth temperature when the remaining p-type GaN contact layer 7 is grown. Here, the heat treatment temperature is 1200 ° C., and the heat treatment time is 60 minutes. In addition, diffusion of impurities can be promoted by further adding a gas containing hydrogen to the N ₂ gas atmosphere.

  Further, in place of impurity diffusion or ion implantation with Mg, at least one kind of impurity among a group of p-type impurities composed of Be, Mg, Ca, and Zn may be selectively diffused or ion-implanted.

(3) Re-growth pretreatment Thereafter, the MgO film and the SiN protective film 16 which are diffusion sources are removed using a hydrofluoric acid-based etching solution. When the AlN protective layer 17 is provided, the AlN protective layer 17 is also removed.

  Then, a heat treatment before the growth of the p-type GaN contact layer 7 (cleaning process of the surface of the p-type AlGaN cladding layer 6) is performed.

(4) Growth of p-type GaN contact layer 7 The p-type GaN contact layer 7 is grown by doping Mg, which is a p-type impurity, while using the MOCVD method again. At this time, in addition to ammonia, a hydrazine derivative is simultaneously supplied as a nitrogen supply source. The growth temperature of the same layer 7 is 1000 ° C.

  The following processes and all the growth temperatures are the same as those in the first embodiment.

  According to the manufacturing method of the present embodiment, the p-type AlGaN cladding layer 6 exists as the uppermost layer during the execution of the process of forming the window region 12, so that the MQW is higher than in the case of the first embodiment. Since the active layer 4 is farther away from the surface of the uppermost layer at this stage, the active layer 4 is less susceptible to surface deterioration due to high-temperature heat treatment for forming the window region 12.

  As a result, the window region 12 without light loss can be realized without causing an increase in operating voltage, and the crystallinity of the region near the MQW active layer 4 is deteriorated by the high-temperature heat treatment in the process of forming the window region 12. Therefore, it is possible to avoid the deterioration of the laser characteristics, and it becomes easier to realize high output and high reliability of the nitride semiconductor laser.

(Embodiment 6)
This embodiment is a modification of the fifth embodiment, and the improvement is that a pulse laser beam or a high energy electron beam is selectively irradiated instead of the solid phase diffusion of impurities in the fifth embodiment. Thus, a region to be the window region 12 is formed by introducing lattice defects locally in the MQW active layer 4.

  After selective irradiation with a pulse laser beam or a high-energy electron beam, high-temperature heat treatment at a temperature of 1200 ° C. is performed in an atmosphere composed of hydrogen gas and nitrogen gas. As a result of the mutual diffusion of lattice defects introduced locally in the MQW active layer 4 by this high-temperature heat treatment, a window corresponding to the laser end face formation planned portion 14 and its peripheral region in the MQW active layer 4 is formed in the window. A disordered region, region 12, is created (selective attraction of the disordered region).

  As a result, it is possible to realize a window region without light loss without causing an increase in operating voltage, and since there is no light absorption by impurities, it becomes possible to oscillate laser without further impairing efficiency. It becomes easier to realize high output and high reliability of the semiconductor laser.

(Appendix)
While the embodiments of the present invention have been disclosed and described in detail above, the above description exemplifies aspects to which the present invention can be applied, and the present invention is not limited thereto. In other words, various modifications and variations to the described aspects can be considered without departing from the scope of the present invention.

  The present invention is suitable for application to, for example, a blue-violet semiconductor laser used for recording or reading a Blu-ray disc or a blue semiconductor laser used for a laser TV.

1 n-type GaN substrate, 2 n-type AlGaN cladding layer, 3 n-type GaN guide layer, 4 MQW active layer, 5 undoped GaN guide layer, 6 p-type AlGaN cladding layer, 7 GaN p-type top layer, 8 insulating film, 9 p Side electrode, 10 n side electrode, 11 n-type impurity solid phase diffusion region, 12 window region, 13 ridge waveguide, 14 laser end face formation planned portion, 15 SiO ₂ film, 16 protective film, 17 AlN protective layer.

Claims (15)

An n-type doped layer step of forming an n-type doped layer on the substrate;
Forming an undoped layer including an active layer on the n-type doped layer; and
A window region forming step with heat treatment, which changes optical characteristics at a predetermined position of the active layer, which later becomes a window region of a nitride-based semiconductor laser;
A p-type uppermost layer forming step of forming a p-type uppermost layer on the undoped layer at a temperature equal to or lower than a maximum heat treatment temperature of the window region forming step using a gas containing a hydrazine derivative after the window region forming step;
And a step of forming a p-side electrode in contact with the p-type uppermost layer,
A method of manufacturing a nitride semiconductor laser.   The window region forming step includes a step of selectively diffusing at least one impurity of a group of n-type impurities composed of B, C, O, Si, P, and S by performing heat treatment. The method for manufacturing a nitride-based semiconductor laser according to claim 1.   The window region forming step includes a step of selectively ion-implanting at least one impurity of a group of n-type impurities composed of B, C, O, Si, P, and S. Item 2. A method for producing a nitride semiconductor laser as described in Item 1.   The method for manufacturing a nitride semiconductor laser according to claim 1, wherein the window region forming step includes a step of selectively irradiating a pulse laser beam or an electron beam. The active layer has a first undoped layer of a multiple quantum well of In _x Ga _(1-x) N / In _y Ga _(1-y) N (x> y, x> 0, y ≧ 0). The method for manufacturing a nitride semiconductor laser according to claim 1, wherein the method is characterized in that: The undoped layer includes a second undoped layer made of GaN or Al _z Ga _(1-z) N (0 ≦ z <1) on the first undoped layer. A method for manufacturing a nitride-based semiconductor laser according to claim 5.   The method of manufacturing a nitride semiconductor laser according to claim 6, wherein a thickness of the second undoped layer is 10 nm or more and less than 100 nm.   The nitride-based semiconductor according to claim 1, wherein the window region forming step forms a window region in a state where a polycrystalline or amorphous AlN protective layer is formed on the undoped layer. Laser manufacturing method.   2. The method of manufacturing a nitride semiconductor laser according to claim 1, wherein the window region forming step is performed after a p-type doped layer is formed on the undoped layer.   The window region forming step includes a step of selectively diffusing at least one impurity of a group of p-type impurities composed of Be, Mg, Ca, and Zn by performing a heat treatment. Item 10. A method for producing a nitride semiconductor laser as described in Item 9.   10. The method of claim 9, wherein the window region forming step includes a step of selectively ion-implanting at least one impurity of a group of p-type impurities composed of Be, Mg, Ca, and Zn. Manufacturing method of nitride semiconductor laser.   The method for manufacturing a nitride-based semiconductor laser according to claim 9, wherein the window region forming step includes a step of irradiating either one of a pulsed laser beam and an electron beam onto an end surface portion of the active layer. .   2. The method of manufacturing a nitride semiconductor laser according to claim 1, wherein the highest processing temperature in the p-type uppermost layer forming step is set to be 100 ° C. or more lower than the highest processing temperature in the window region forming step. .   2. The method of manufacturing a nitride semiconductor laser according to claim 1, wherein the highest temperature processing in the window region forming step is performed in a gas atmosphere containing nitrogen and hydrogen. A substrate,
An n-type doped layer provided on the substrate;
An undoped layer including an active layer provided on the n-type doped layer;
Window regions provided at predetermined positions on both ends of the active layer;
A p-type uppermost layer provided on the undoped layer;
A p-side electrode in contact with the p-type top layer;
The carbon concentration of the p-type uppermost layer is 5 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ¹⁸ cm ⁻³ or less,
The p-type impurity concentration of the p-type uppermost layer is less than twice the p-type impurity concentration near the center of the nitride-based semiconductor laser,
Nitride semiconductor laser.

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